James D. Watson once said that he and Francis Crick had no doubt that their proposed DNA structure was essentially correct, because the structure was so beautiful it had to be true! At an internet site accessed by the keyword DNA you can view a large collection of different types of models of DNA structure. Some models highlight the sugar-phosphate backbones, others the A—T and G—C base pairs, still others the helical structure of double-stranded DNA.

With proper dietary control of blood phenylalanine, patients with PKU can develop normally and lead normal lives. When dietary control is relaxed, however, blood phenylalanine returns to high levels. This situation is extremely dangerous for a developing fetus, resulting in high risk of congenital heart disease, small head size, mental retardation, and slow growth. Affected children are said to have maternal PKU. They are affected, not because of their own inability to metabolize phenylalanine, but because of high levels of phenyalanine in their mothers' blood. The risk can be reduced, but not entirely eliminated, if PKU mothers plan their pregnancies and adhere to a strict dietary regimen prior to and during pregnancy. To learn more about this unanticipated consequence of dietary treatment of PKU, log onto the phenylalanine hydroxylase knowledge database at the keyword site.

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